Countertops for use in laboratories must withstand severe environmental conditions. They must be resistant to strong chemicals such as solvents, acids and corrosive compositions, and they must also withstand severe physical conditions such as impacts and localized heating without breaking or cracking. The countertop must have a smooth, impermeable surface which is easy to clean. To meet these demanding performance requirements, many laboratory countertops have been formed from an epoxy composition. Typically, the countertop comprises a thick slab of cured epoxy resin containing a mineral filler. The slabs are cast in thicknesses of approximately 1 inch to 11/2 inches, in lengths of up to 8 feet and in widths of up to 4 feet. Epoxy countertops of this general type have performed quite well under the demanding environmental conditions encountered in laboratories, and have been used extensively. Indeed, this type of countertop is used in most academic and industrial laboratory countertop installations. However, a drawback to this type of countertop is that it is quite heavy. A typical epoxy countertop slab may weigh 10 pounds or more per square foot. Thus, the material cost and shipping expense is significant and the weight also makes handling and installation difficult.
Thinner sheets of an epoxy composition on the order of about 1/4 to 3/8 inch thick have been produced for use in less demanding installations, for example as liners for fume hoods, by casting in an open horizontal mold. However, this method is incapable of meeting the exacting dimensional tolerances and flatness requirements of countertop applications. Also, the requirements for impact resistance and heat resistance are less severe in fume hood liner applications than in countertop applications.
Other methods which have been proposed for producing thin resin sheet materials include pressure gelation and compression molding. However, these methods have drawbacks or limitations which make them impractical or uneconomical for countertop applications.